Valves for the control of a flow of gas are especially used in ventilating systems, especially for crankcases of combustion engines. There, they are arranged in the main streaming way of the gases from the crankcase to a suction compartment of the combustion engine, through which the blow-by gases of the combustion engine are guided back to the suction compartment.
Pressures control valves are however not only used in these areas. In general, they are used for the pressure reduction and control in gas ducts. According to the state of the art, pressure control valves comprise a connection that is charged with negative pressure (an outlet) and a connection that is charged with overpressure (inlet). Using a control membrane, a closing body is actuated which closes and opens, respectively, a valve opening arranged within the valve. The pressure on the inlet and outlet of the valve is set dependent on the pressures and therefore the forces which charge the pressure control membrane. This, for instance in the crankcase ventilation duct of a combustion engine aims on maintaining an allowed pressure, usually a small negative pressure relative to the atmospheric outside pressure whereas both too high and too negative pressure values inside of the crankcase have to be avoided.
Simple pressure control valves known in the state of the art in their open state need to have a small flow resistance for the flowing gases so that the outlet cross section (especially of the valve opening) has to be chosen large if possible.
The closing and opening behaviour of a pressure control valve can be described by help of a load deflection curve. The load deflection curve which in its course describes the closed and the opened state of the valve is obtained for a particular pressure control valve for a crankcase ventilation by plotting the suction pressure on the outlet to the x-coordinate and the overpressure at the inlet to the y-coordinate. There, it is assumed that in the negative x-direction, more negative thus higher suction pressures and in the positive y-direction, higher pressures at the inlet of the valve or at another position within the valve are plotted.
The area of the load deflection curve which describes the completely open state of the valve corresponds to a line through the origin in the first and third quadrant of the Cartesian coordinate system. If in the flow way of the valve between the inlet and the outlet, pressure reducing elements are present this leads to a vertical upward shift of the load deflection line. Such pressure reducing elements in this area of the curve thus cause a y-intercept different from zero.
In the third quadrant this load deflection line passes into an area which describes an increasingly closed state of the valve. This zone of the deflection line of the valve depends on the ratio of the areas of the effective area of the control membrane, which is charged with the present pressure and the outlet cross section of the valve opening onto which in the closed state the outlet-sided pressure acts. This area should be as large as possible, in order that the load deflection line of the valve in this area is as flat as possible, thus preferably parallel to the abscissa. For a high ratio of areas however, the membrane has to be very large and/or the cross section of the valve opening to be small. A small outlet cross section is in contradiction to the above mentioned requirement of a large outlet cross section. Moreover, a large membrane is related to the drawbacks of high cost and large-volume structural shape.
Even with a relatively flat load deflection line, with conventional pressure control valves, it is still possible that due to further flow resistances arranged in the ventilation duct, such as oil separators, with high volume streams, unacceptably high pressures occur in the crankcase. By use of a spring which counteracts the closing of the valve, it is possible to reduce the unacceptably high pressure values to a predetermined value. This is however related to the drawback that at low volume streams, unacceptably low pressures can occur in the crankcase, as the force provided by the spring for counteracting the closure has to be overcome first.
Therefore, it is the object of the present invention to provide a valve that prevents from the above mentioned problems and especially provides an opportunity to regulate the outlet-sided pressures in such a way that they remain the same or almost the same independent of the volume stream guided through the valve at otherwise unchanged conditions. It is a further object of the present invention to provide a corresponding ventilation system, a corresponding combustion engine and a corresponding use of the valve according to the invention.
The above objects are achieved by the invention defined in the appended independent claims. Advantageous embodiments of the valve according to the invention as well as of the ventilation system according to the invention are given in the respective subordinate claims.
EP 0 724 206 A2 shows a valve where in addition to the control membrane an auxiliary membrane is given. This auxiliary membrane on one of its sides is charged with the suction pressure as it statically results at the valve disk and on its other side is charged with the atmospheric pressure as the reference pressure. Under normal operating conditions, at which the suction pressure is smaller than the reference pressure, the auxiliary membrane counteracts the closure movement of the valve. EP 0 724 206 A2 further describes that through use of such an auxiliary membrane, the pressure inside of the crankcase can be regulated more independent of the suction pressure in the intake section.
DE 103 21 211 A1 discloses a valve where in addition to the control membrane, an additional membrane is given as well. In contrast to EP 0 724 206 A2, the additional membrane on one of its sides is charged with a force produced in an electromagnetic balancing device that is independent of the crankcase pressure and on its other side by the atmospheric pressure as a reference pressure. By a mechanical coupling of the additional membrane with the control membrane, the force produced by the balancing device is transferred to the control membrane and counteracts the closure direction of the valve.
DE 100 44 922 B4 shows a further valve arrangement in which the crankcase pressure of a combustion engine is controlled by a throttle valve. The throttle valve comprises a control membrane, which on one of its sides is charged with the atmospheric pressure as a reference pressure and on its other side with the crankcase pressure. The control membrane thus divides the membrane chamber into an upper and a lower membrane chamber part. Below this partition which borders the lower membrane chamber part downwards, a valve chamber is given, which contains a valve seat connected with the suction section and which can be closed with a valve body and a valve body actuating element. The valve chamber further has a fluidic connection with the ventilation duct of the combustion engine, where an oil separator is arranged in the course of the ventilation duct. The valve body actuating element is linked to the control membrane and penetrates the partition between the lower membrane chamber and the valve chamber. The sealed penetration of the valve body actuating element through the partition there is assured by use of a sealing membrane, the effective area of which is rather small compared to the effective area of the control membrane. This is supposed to reduce the influence of additional forces acting at the sealing membrane on the control membrane.
Starting at such a valve as it is described in EP 0 724 206 A2, the present invention has the diverging object to control the inlet-sided pressure of the valve as independent as possible of the gas volume stream in the valve.